Method and system for determining shutter fluttering sequence

ABSTRACT

A method, system and computer-usable medium for determining shutter fluttering sequence. The disclosed approach is based on the use of shutter flutter technology, which means that an image can be acquired in such a manner as to encode all information about the moving subject. The disclosed approach involves determining a shutter&#39;s fluttering pattern that optimally encodes information at all frequencies. The disclosed approach involves an optimization method for finding a shutter fluttering pattern that has several desired properties. These properties can be expressed in the context of a fitness function: given a fluttering pattern and the target subject&#39;s velocity, it produces the equivalent Modulation Transfer Function (MTF), measures three attributes, and produces a fitness score. These attributes are the minimum contrast, the variance in contrast across spatial frequencies, and the mean contrast. The objective of the disclosed approach is to determine the fluttering pattern that maximizes the fitness score.

CROSS-REFERENCE TO PROVISIONAL APPLICATION

This application claims the benefit of priority based on U.S.Provisional Patent Application Ser. No. 61/156,739 filed Mar. 2, 2009,entitled “Method and System for Determining Shutter FlutteringSequence.” The above-referenced provisional patent application is herebyincorporated by reference herein in its entirety.

STATEMENT OF GOVERNMENT RIGHTS

The invention disclosed in this application was made with Governmentsupport under Contract Number W91CRB-09-C-0013 awarded by the U.S. ArmyResearch Office. The Government has certain rights in the invention.

TECHNICAL FIELD

Embodiments are generally related to the field of security systems andbiometric identification. Embodiments are also related to iris-based andface recognition biometric authentication methods and systems.Embodiments are additionally related to flutter shutter technology.Embodiments are additionally related to image-processing techniques,devices, and systems.

BACKGROUND OF THE INVENTION

Acquiring sharply-focused images of moving people or objects is afundamental and challenging problem in several surveillanceapplications, particularly iris-based biometrics and face recognition.

Iris recognition is a method of biometric authentication that utilizespattern recognition techniques based on high-resolution images of theirises of an individual's eyes. Iris recognition relies on cameratechnology with subtle infrared illumination reducing specularreflection from the convex cornea to create images of the detail-rich,intricate structures of the iris. Converted into digital templates,these images provide mathematical representations of the iris that yieldunambiguous positive identification of an individual.

Iris recognition has been recently recognized and gained much attentiondue to its high reliability in identifying humans. Its suitability as anexceptionally accurate biometric derives from its extremely data-richphysical structure, genetic independence (no two eyes are the same evenfor twins), stability over time, and non-contact means (a featureimportant for non-cooperative subjects).

Facial recognition typically involves the use of a computer applicationfor automatically identifying or verifying a person from a digital imageor a video frame from a video source. One of the ways to accomplish thisis by comparing selected facial features from the image and a facialdatabase.

One type of device that has been found in use in biometricidentification and authentication is the flutter shutter camera, basedon flutter shutter technology. Note that a non-limiting example of aflutter shutter camera and flutter shutter technology in general isdisclosed in U.S. Patent Application Publication Serial No.US2007/0258707A1, entitled “Method and Apparatus for Deblurring Images,”which published to Ramesh Raskar on Nov. 8, 2007, and is incorporatedherein by reference. Another non-limiting example of a flutter shuttercamera and flutter shutter technology is disclosed in U.S. PatentApplication Publication Serial No. US2007/0258706A1, entitled “Methodfor Deblurring Images Using Optimized Temporal Coding Patterns,” whichpublished to Ramesh Raskar, et al on Nov. 8, 2007, and is incorporatedherein by reference.

Iris-based biometric identification thus has great potential to enhancecontrolled access and even surveillance of high security areas. Much ofthis potential can only be realized by acquiring iris images fromnon-cooperative subjects. Like other applications that exploit visualinformation, however, iris-based biometrics is limited by the ability toacquire high-quality images in certain situations. One situation that isparticularly challenging is the acquisition of sharply-focused irisimages from moving subjects. Given a modest amount of light, as iscommon indoors, relatively long exposures are necessary at even thewidest aperture setting. For moving subjects, this producesmotion-blurred images which lack much of the crucial high-frequencyinformation needed to perform iris matching.

For an application like iris recognition, wherein fine scale featuresare essential to proper classification, the use of a traditional shutterimposes some fundamental limits on the extent of motion blur that can betolerated. Motion blur, as through a traditional shutter, is equivalentto convolution of a sharply-focused image with a box filter.Motion-blurred images of this type lack information regarding the objectat a number of spatial frequencies. This lack of information isirreversible and no post processing can recover it from the image.Methods that attempt to deblur the image will severely amplify sensornoise, hallucinate content, or both. Though it may be useful inimproving subjective image quality, hallucinating image content iscounter-productive for forensic applications, and amplifying noisecomplicates iris matching.

To avoid this loss of information during image capture, some prior artapproaches have advocated the use of a fluttering shutter anddemonstrated the ability to recover high-quality images despite blurfrom moving objects. During exposure, the camera's shutter fluttersbetween open and closed while exposure is accumulated on the sensor.This produces an image with coded blur which, unlike traditional blur,conveys information about the subject at all spatial frequencies. Givena suitably designed processing method that is based on the shutter'sfluttering pattern, deblurring recovers an image with low levels ofnoise while avoiding reconstruction artifacts.

In moderate and low lighting conditions, however, the need to use longexposure times causes images of moving subjects to be significantlydegraded by blur. This blur will destroy fine details of, for example,the subject's iris to an extent that the iris image will be useless foridentification. It is therefore necessary to design systems that arecapable of acquiring sharp images of subjects despite low lightingconditions and subject motion.

BRIEF SUMMARY

The following summary is provided to facilitate an understanding of someof the innovative features unique to the embodiments disclosed and isnot intended to be a full description. A full appreciation of thevarious aspects of the embodiments can be gained by taking the entirespecification, claims, drawings, and abstract as a whole.

It is, therefore, one aspect of the present invention to provide for amethod and system for enhanced biometric identification.

It is another aspect of the present invention to provide for an enhancedshuttering method and system.

It is yet a further aspect of the present invention to provide for amethod and system for determining a shutter fluttering sequence.

The aforementioned aspects and other objectives and advantages can nowbe achieved as described herein. A method and system for determiningshutter fluttering sequence is disclosed. The disclosed approach isbased on the use of shutter flutter camera technology, which means thatan image can be acquired in such a manner as to encode all informationabout the moving subject. The disclosed approach involves determining ashutter's fluttering pattern that optimally encodes information at allfrequencies. Previous approaches to determining such a shutter wereincapable of incorporating constraints arising from the particularcamera hardware and make the further unreasonable assumption that theshortest available open shutter time is sufficiently short to stopmotion. The disclosed approach avoids these problems and identifiesshutter patterns that can directly be utilized by a camera and software.

The disclosed approach involves optimization method for finding ashutter fluttering pattern that has several desired properties. Theseproperties can be expressed in the context of a fitness function: givena fluttering pattern and the target subject's velocity, it produces theequivalent Modulation Transfer Function (MTF), measures threeattributes, and produces a fitness score. These attributes are theminimum contrast, the variance in contrast across spatial frequencies,and the mean contrast. The objective of the disclosed approach is todetermine the fluttering pattern that maximizes the fitness score.

As with most interesting problems, the space of potential flutteringpatterns is prohibitively large to search exhaustively. One of the keysto the disclosed approach is that the search for the optimal (or anear-optimal) fluttering pattern can be made tractable by decomposingthe search into a two-step process. The fluttering pattern is completelyspecified by knowing (1) the number and duration of each open shutterperiod and (2) the start time of each such open shutter period. Theinvented method performs the search for the near-optimal pattern bydetermining these two properties sequentially. It first determines thenumber and duration of open shutter periods using the observation thatthis choice determines the envelope on the MTF (i.e. an upper bound onthe contrast at each spatial frequency).

Given a particular collection of open shutter periods that produces anenvelope with good fitness, the second step determines the arrangementof those open shutter periods in the flutter pattern. This is achievedby creating an initial, naïve arrangement, and then by modifying thatarrangement in a number of ways (while preserving the validity of thesequence) that improve the fitness score. Given methods that performthis modification, this second optimization step can be performed usinga number of well-known computational techniques (hill climbing,simulated annealing, etc.).

At a high level, the disclosed embodiments take as input two parameters:the required exposure time (this will be the sum of the durations of theopen shutter periods) and the subject velocity (measured in pixels permillisecond). The disclosed embodiments incorporate hardware constraintsby respecting the minimum allowable open shutter duration. Its output isthe fluttering pattern (for use with the camera control software), alongwith the equivalent MTF, point spread function (PSF), and fitness score(for analytic use).

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying figures, in which like reference numerals refer toidentical or functionally-similar elements throughout the separate viewsand which are incorporated in and form a part of the specification,further illustrate the embodiments and, together with the detaileddescription, serve to explain the embodiments disclosed herein.

FIG. 1 illustrates a schematic view of a data-processing system whichincludes the use of a biometric reader, which may incorporate the useof, for example, a camera, in accordance with an example embodiment.

FIG. 2 illustrates a schematic view of a software system including anoperating system, application software, and a user interface, inaccordance with an example embodiment.

FIG. 3 depicts a graphical representation of a network ofdata-processing systems, which may be utilized in accordance with anexample embodiment;

FIG. 4 illustrates a high-level flow chart of operations depictinglogical operational steps of a method of determining a shutterfluttering sequence, in accordance with an example embodiment; and

FIG. 5 illustrates a high-level flow chart of operations depictinglogical operational steps of a method of determining a shutterfluttering sequence, in accordance with a preferred example embodiment.

DETAILED DESCRIPTION

The particular values and configurations discussed in these non-limitingexamples can be varied and are cited merely to illustrate at least oneembodiment and are not intended to limit the scope thereof.

FIGS. 1-3 are provided as exemplary diagrams of data-processingenvironments, which can be implemented in accordance with one or moreexample embodiments. It should be appreciated that FIGS. 1-3 are onlyexemplary and are not intended to assert or imply any limitation withregard to the environments in which aspects of the disclosed exampleembodiments may be implemented. Many modifications to the depictedenvironments may be made without departing from the spirit and scope ofthe disclosed example embodiments.

As depicted in FIG. 1, a data-processing system 100 can include, forexample, a central processor 101, a main memory 102, an input/outputcontroller 103, a keyboard 104, a pointing device 105 (e.g., mouse,track ball, pen device, or the like), a display device 106, and a massstorage component 107 (e.g., hard disk). A camera 108 may be employed tocommunicate with the data-processing system 100. Camera 108 can beimplemented as, for example, a flutter shutter camera, which may beemployed in the context of a biometric authentication system such as,for example, an iris and/or facial biometric recognition system ordevice. A flutter shutter camera can be configured as a camera capableof capturing moving objects at an exposure time of, for example, over 50milliseconds, like high speed motion cameras. Using a coded exposuresequence, the flutter shutter camera can recover, for example, text froma speeding car and sharpen images. As illustrated, the variouscomponents of the example embodiment of data-processing system 100 cancommunicate through a system bus 110 or similar architecture.

FIG. 2 illustrates a computer software system 150 for directing theoperation of the data-processing system 100 depicted in FIG. 1. Softwaresystem 150, which is stored in system memory 102 and on disk memory 107,can include a kernel or operating system 151 and a shell or interface153. One or more application programs, such as application software 152,may be “loaded” (i.e., transferred from storage 107 into memory 102) forexecution by the data-processing system 100. The data-processing system100 receives user commands and data through user interface 153; theseinputs may then be acted upon by the data-processing system 100 inaccordance with instructions from operating module 151 and/orapplication module 152.

The interface 153, which is preferably a graphical user interface (GUI),can also serves to display results, whereupon the user may supplyadditional inputs or terminate a given session. In one possibleembodiment, operating system 151 and interface 153 can be implemented inthe context of a “Windows” system. It can be appreciated, of course,that other types of systems are possible. For example, rather than atraditional “Windows” system, other operation systems such as, forexample, Linux may also be employed with respect to the operating system151 and interface 153. Application module 152, on the other hand, caninclude instructions such as the various operations described hereinwith respect to the various components and modules described herein suchas, for example, the methods 400 and 500 depicted respectively in FIGS.4-5.

FIG. 3 illustrates a graphical representation of a network of dataprocessing systems in which aspects of the present invention may beimplemented. Network data processing system 300 can be provided as anetwork of computers in which embodiments of the present invention maybe implemented. Network data processing system 300 contains network 302,which can be utilized as a medium for providing communications linksbetween various devices and computers connected together within networkdata processing system 100. Network 302 may include connections such aswired, wireless communication links, fiber optic cables, USB cables,Ethernet connections, and so forth.

In the depicted example, server 304 and server 306 connect to network302 along with storage unit 308. In addition, clients 310, 312, and 314connect to network 302. These clients 310, 312, and 314 may be, forexample, personal computers or network computers. Data-processing system100 depicted in FIG. 1 can be, for example, a client such as client 310,312, and/or 314. Alternatively, data-processing system 100 can beimplemented as a server such as servers 304 and/or 306, depending upondesign considerations.

In the depicted example, server 304 provides data such as boot files,operating system images, and applications to clients 310, 312, and 314.Clients 310, 312, and 314 are clients to server 304 in this example.Network data processing system 300 may include additional servers,clients, and other devices not shown. Specifically, clients may connectto any member of a network of servers which provide equivalent content.

In some embodiments, network data processing system 300 may be theInternet with network 302 representing a worldwide collection ofnetworks and gateways that use the Transmission ControlProtocol/Internet Protocol (TCP/IP) suite of protocols to communicatewith one another. At the heart of the Internet is a backbone ofhigh-speed data communication lines between major nodes or hostcomputers, consisting of thousands of commercial, government,educational, and other computer systems that route data and messages. Ofcourse, network data processing system 300 also may be implemented as anumber of different types of networks such as, for example, a secureintranet, a local area network (LAN), or a wide area network (WAN). FIG.1 is intended as an example and not as an architectural limitation fordifferent embodiments of the present invention.

The following description is presented with respect to embodiments ofthe present invention, which can be embodied in the context of adata-processing system such as data-processing system 100, computersoftware system 150, data-processing system 300, and network 302depicted respectively FIGS. 1-3. The present invention, however, is notlimited to any particular application or any particular environment.Instead, those skilled in the art will find that the system and methodsof the present invention may be advantageously applied to a variety ofsystem and application software, including database management systems,word processors, and the like. Moreover, the present invention may beembodied on a variety of different platforms, including Macintosh, UNIX,LINUX, and the like. Therefore, the description of the exemplaryembodiments, which follows, is for purposes of illustration and notconsidered a limitation.

FIG. 4 illustrates a high-level flow chart of operations depictinglogical operational steps of a method 400 of determining a shutterfluttering sequence, in accordance with a preferred embodiment. Notethat the method 400 of FIG. 4 and method 500 of FIG. 5, and othermethodologies disclosed herein, can be implemented in the context of acomputer-useable medium that contains a program product. Programsdefining functions on the present invention can be delivered to a datastorage system or a computer system via a variety of signal-bearingmedia, which include, without limitation, non-writable storage media(e.g., CD-ROM), writable storage media (e.g., hard disk drive,read/write CD ROM, optical media), system memory such as, but notlimited to, Random Access Memory (RAM), and communication media such ascomputer and telephone networks including Ethernet, the Internet,wireless networks, and like network systems.

It should be understood, therefore, that such signal-bearing media whencarrying or encoding computer readable instructions that direct methodfunctions in the present invention, represent alternative embodiments ofthe present invention. Further, it is understood that the presentinvention may be implemented by a system having means in the form ofhardware, software, or a combination of software and hardware asdescribed herein or their equivalent. Thus, the methods 400 and 500, forexample, described herein can be deployed as process software in thecontext of a computer system or data-processing system as that depictedin FIGS. 1-3.

Note that the disclosed embodiments describe and illustrate anoptimization method for finding a shutter fluttering pattern that hasseveral desired properties. As indicated at block 402, the processbegins. Such properties can be expressed in the context of a fitnessfunction. As illustrated at block 404, given a fluttering pattern and atarget subject's velocity, the equivalent Modulation Transfer Function(MTF) can be generated. Thereafter, as depicted at block 406, anoperation can be processed for measuring three attributes, andthereafter, as indicated at block 408, producing a fitness score. Thethree attributes are the minimum contrast as indicated at block 405, thevariance in contrast across spatial frequencies as illustrated at block407, and the mean contrast as illustrated at block 409. The objective ofmethod 400 is to determine the fluttering pattern that maximizes thefitness score. The process can then terminate, as indicated at block410.

As with most interesting problems, the space of potential flutteringpatterns is prohibitively large to search exhaustively. One of the keysto the approach described herein is that the search for the optimal (ora near-optimal) fluttering pattern can be made tractable by decomposingthe search into a two-step process.

FIG. 5 illustrates a high-level flow chart of operations depictinglogical operational steps of a method 500 of determining a shutterfluttering sequence, in accordance with a preferred embodiment. Notethat method 500 depicted in FIG. 5 represents a further refinement tothe general methodology of method 400. As indicated by the approach ofmethod 500 depicted in FIG. 5, the fluttering pattern can be completelyspecified by determining (1) the number and duration of each openshutter period, and (2) the start time of each such open shutter period.The process generally begins, as illustrated at block 502.

The instructions of method 500 perform the search for the near-optimalpattern by determining these two properties sequentially. The approachof method 500 first determines the number and duration of open shutterperiods using the observation that this choice determines the envelopeon the MTF (i.e. an upper bound on the contrast at each spatialfrequency), as indicated at block 504. Given a particular collection ofopen shutter periods that produces an envelope with good fitness, thesecond step, as indicated at block 506, determine the arrangement ofthose open shutter periods in the flutter pattern. This can be achievedby creating an initial, naïve arrangement, and then by modifying thatarrangement in any one of a number of approaches (while preserving thevalidity of the sequence) that improve the fitness score. Given methodsthat perform this modification, this second optimization step can beperformed using a number of well-known computational techniques (hillclimbing, simulated annealing, etc.). Thus, process can then terminate,as indicated at block 508.

At a high level, the methods 400 and 500 receive as input, twoparameters: the required exposure time (this will be the sum of thedurations of the open shutter periods) and the subject velocity(measured in pixels per millisecond). The approach of methods 400 and500 incorporate hardware constraints by respecting the minimum allowableopen shutter duration. The output of methods 400 and 500 is thefluttering pattern (for use with the camera control software), alongwith the equivalent MTF, point spread function (PSF), and fitness score(for analytic use).

While the present invention has been particularly shown and describedwith reference to a preferred embodiment, it will be understood by thoseskilled in the art that various changes in form and detail may be madetherein without departing from the spirit and scope of the invention.Furthermore, as used in the specification and the appended claims, theterm “computer” or “system” or “computer system” or “computing device”or “data-processing system” includes any data-processing apparatusincluding, but not limited to, personal computers, servers,workstations, network computers, main frame computers, routers,switches, Personal Digital Assistants (PDA's), telephones, and any othersystem capable of processing, transmitting, receiving, capturing and/orstoring data.

It will be appreciated that variations of the above-disclosed and otherfeatures and functions, or alternatives thereof, may be desirablycombined into many other different systems or applications. It will alsobe appreciated, that various presently unforeseen or unanticipatedalternatives, modifications, variations or improvements therein may besubsequently made by those skilled in the art, which are also intendedto be encompassed by the following claims.

What is claimed is:
 1. A method for fluttering a shutter according to adetermined shutter fluttering sequence, said method comprising:determining a modulation transfer function based on a particular shutterfluttering pattern and at least two properties associated with a targetsubject, said particular shutter fluttering pattern associated with aflutter shutter camera; determining a minimum allowable open shutterduration for said flutter shutter camera; measuring a plurality ofattributes associated with said modulation transfer function, saidmeasured attributes being combined to produce a fitness score;identifying a fluttering pattern that maximizes said fitness score;selecting a shutter fluttering sequence with respect to said shutterflutter and said target subject according to said fluttering patternthat maximizes said fitness score; and communicating said shutterfluttering sequence to said flutter shutter camera in order to fluttersaid shutter of said flutter shutter camera according to said shutterfluttering sequence.
 2. The method of claim 1 wherein identifying afluttering pattern that maximizes said fitness score, further comprisesspecifying said fluttering pattern by sequentially: first determining anumber and a duration of each open shutter period with respect to atleast one constraint associated with said flutter shutter camera; andsecond identifying a start time of each open shutter period.
 3. Themethod of claim 1 wherein said at least one property associated withsaid target subject comprises a velocity of said target subject.
 4. Themethod of claim 1 wherein at least one attribute among said plurality ofattributes comprises a minimum contrast.
 5. The method of claim 1wherein at least one attribute among said plurality of attributescomprises a variance in contrast across a plurality of spatialfrequencies.
 6. The method of claim 1 wherein at least one attributeamong said plurality of attributes comprises a mean contrast.
 7. Themethod of claim 1 further comprising: capturing an image of said targetsubject from among a plurality of subjects in said image via saidflutter shutter camera.
 8. The method of claim 7 further comprising:utilizing said shutter fluttering sequence with respect to said fluttershutter camera and said target subject; and biometrically identifyingsaid target subject among said plurality of subjects.
 9. A system forfluttering a shutter according to a determined shutter flutteringsequence, said system comprising: a flutter shutter camera; a processor;a data bus coupled to the processor; and a computer-usable mediumembodying computer code, the computer-usable medium being coupled to thedata bus, the computer program code comprising instructions executableby the processor and configured for: determining a modulation transferfunction based on a particular shutter fluttering pattern and at leasttwo properties associated with a target subject, said particular shutterfluttering pattern associated with said flutter shutter camera;determining a minimum allowable open shutter duration for said fluttershutter camera; measuring a plurality of attributes associated with saidmodulation transfer function, said measured attributes being combined toproduce a fitness score; identifying a fluttering pattern that maximizessaid fitness score; selecting a shutter fluttering sequence with respectto said shutter flutter and said target subject according to saidfluttering pattern that maximizes said fitness score; and communicatingsaid shutter fluttering sequence to said flutter shutter camera in orderto flutter said shutter of said flutter shutter camera according to saidshutter fluttering sequence.
 10. The system of claim 9 wherein saidinstructions for identifying a fluttering pattern that maximizes saidfitness score are further configured to specify said fluttering patternby sequentially: first determining a number and a duration of each openshutter period with respect to at least one constraint of said fluttershutter camera; and second identifying a start time of each open shutterperiod.
 11. The system of claim 9 wherein said at least one propertyassociated with said target subject comprises a velocity of said targetsubject.
 12. The system of claim 9 wherein at least one attribute amongsaid plurality of attributes comprises a minimum contrast.
 13. Thesystem of claim 9 wherein at least one attribute among said plurality ofattributes comprises a variance in contrast across a plurality ofspatial frequencies.
 14. The system of claim 9 wherein at least oneattribute among said plurality of attributes comprises a mean contrast.15. The system of claim 9 wherein said instructions are furtherconfigured for capturing an image of said target subject from among aplurality of subjects in said image via said flutter shutter camera. 16.The system of claim 15 wherein said instructions are further configuredfor utilizing said shutter fluttering sequence with respect to saidflutter shutter camera and said target subject; and biometricallyidentifying said target subject among said plurality of subjects.
 17. Anapparatus for fluttering a shutter according to a determined shutterfluttering sequence, said apparatus comprising: a shutter fluttercamera; and a non-transitory computer-usable medium for determining ashutter fluttering sequence, said computer-usable medium embodyingcomputer program code, said computer program code comprising computerexecutable, instructions configured for: determining a modulationtransfer function based on a particular shutter fluttering pattern andat least two properties associated with a target subject, saidparticular shutter fluttering pattern associated with said fluttershutter camera; determining a minimum allowable open shutter durationfor said flutter shutter camera; measuring a plurality of attributesassociated with said modulation transfer function, said measuredattributes being used to produce a fitness score; identifying afluttering pattern that maximizes said fitness score; selecting ashutter fluttering sequence with respect to said shutter flutter andsaid target subject according to said fluttering pattern that maximizessaid fitness score; and communicating said shutter fluttering sequenceto said flutter shutter camera in order to flutter said shutter of saidflutter shutter camera according to said shutter fluttering sequence.18. The apparatus of claim 17 wherein said embodied computer programcode for identifying a fluttering pattern that maximizes said fitnessscore, further comprises computer executable, instructions forspecifying said fluttering pattern by sequentially: first determining anumber and a duration of each open shutter period with respect to atleast one constraint of said flutter shutter camera; and secondidentifying a start time of each open shutter period.
 19. The apparatusof claim 17 wherein said at least one property associated with saidtarget subject comprises a velocity of said target subject.
 20. Theapparatus of claim 17 wherein at least one attribute among saidplurality of attributes comprises at least one of the following types ofattributes: a minimum contrast, a variance in contrast across aplurality of spatial frequencies, and a mean contrast.